1. Field of the Invention
The invention concerns a process for the production of photopolymerizable flexographic printing plates in which the exposed printing plates are washed out and dried with the image side up and if necessary given a secondary treatment.
2. Description of Related Art
Flexographic printing plates are elastic elevated printing forms with a relief-like surface. To produce this surface the printing plates are first exposed or otherwise treated, at which time, depending on the version, the exposed or unexposed parts polymerize out. The unpolymerized regions are then washed out, if necessary with the aid of brushes.
In a known process of this type (EP 0 225 678 B1) the printing plates with their exposed side down are kept in a continuous motion through a number of series-arranged rotating brushes which dip into a washing fluid. After passing the brushes the printing plates are inverted so that they come to lie with the image side up. Before or during the turn, the remaining fluid is removed by suction. The turned printing plates are then blown on by drying air from above, during which they are pulled past at the same speed as in the case of drying by blow nozzles. Following this drying air treatment the printing plates are turned again and conveyed in the vertical position up to a secondary treatment station where they are given another drying after being turned again so that image side is up once more.
The problem with machines of this type is that the drying usually lasts much longer than the washing out process. Now if the printing plates are conveyed at the same speed through the washing-out section and the drying section, the drying section must have a much greater length than the wash out section. As an alternative to this the washing time can be lengthened or the drying time shortened. Compromises of this type, however, lead to unsatisfactory results. It has also been found that in the known process there are limitations for the operating speed, because in the section in which the printing plates are hanging freely downward, at higher speeds accelerating forces act on the printing plates which lead to an undesired deformation of the printing plates. Since these deformations cannot be controlled, here especially in the case of multi-color printing where a printed image is produced with the aid of several printing plates, undesired changes in the final printed image appear.
DE 32 48 411 C2 shows a device for the multi-step treatment of photo printing plates in which the photo printing plates in a horizontal position are washed out from above with brushes. Then they are suspended on one edge and guided while hanging vertically through various stations where the printing plates are dried and subjected to other chemical treatments. Between the individual stations the hanging printing plate must always be raised and lowered. In this case also the hanging printing plate must absorb the accelerating forces in each case so that the magnitude of the lifting and lowering speeds is limited. The known device also operates with a fixed rhythm. This also limits the fabrication speed of the device.
The invention has the objective of devising a process which permits the production of printing plates at high speeds and with high quality.